1. Field of the Invention
The present invention relates in general to electrodes for use in rechargeable lithium ion batteries, wherein the electrode includes an active material comprising a transition metal oxide having a surface associated with a lithium salt. The lithium salt increases compatibility of the active material with an associated electrolyte to, in turn, increase electrochemical performance of the electrode and associated electrochemical cell. The invention is also directed to a process for fabricating such a modified electrode for use in an electrochemical cell.
2. Background Art
The use of a transition metal oxide as an electrode (such as a cathode) active material between a current collecting substrate and an electrolyte in an electrochemical cell has been know in the art for several years. While such a coating improves electrical conductivity between the current collector and electrolyte, problems nevertheless have been observed with such a coating. Specifically, it is known that transition metal oxides are somewhat unstable with respect to the electrolyte (liquid, gel, plastic or polymer) during cell cycling. Accordingly, such instability results in rate and capacity loss during subsequent cycling and storage.
In an effort to combat such instability, the prior art has identified that inorganic salts, such as inorganic lithium salts, when coated on the surface of a transition metal oxide active material, will serve to stabilize the transition metal oxide relative to the associated electrolyte. Indeed, as identified in an article entitled Phase Stability of LiAlO.sub.2 in Molten Carbonate, published Dec. 12, 1997, J. Electrochem. Soc., Vol. 144, No. 12, LiAlO.sub.2 is a stable component in an associated electrolyte.
Furthermore, Japanese Kokai No. JP 09171813 (Benno, et al.) and Amatucci, U.S. Pat. No. 5,705,291, both disclose that an inorganic lithium salt can be associated with the surface of a transition metal oxide active material so as to result in a stable interface with the associated electrolyte. While stability has been addressed, none of such prior art teaches or suggests the use of an organic component associated with the lithium salt for increasing compatibility of the surface of the active material by the associated electrolyte. Such increased compatibility results in greater direct association between the surface of the active material and electrolyte which, in turn, facilitates increased ionic and electronic charge transfer therebetween.